TGah is a task group (TG) for IEEE 802.11 standard to create specifications for under 1 Gigahertz (GHz) WiFi networks and communications. The TGah WiFi specifications are designed for application in sensor networks. Another or secondary use of such WiFi communications is a scenario of traffic offloading from cellular networks to WiFi networks. One of the requirements of TGah is for an Access Point (AP) to support more than 6,000 associated devices. TGah operates at relatively narrow bandwidth, e.g., 1 and 2 Megahertz (MHz), by downclocking 20 Megahertz (MHz) WiFi implementations. This leads to increased length in a symbol duration from 4 microseconds (μs) in 20 MHz to 40 μs in 2 MHz. The power consumption is another significant factor in sensor networks. Many of the sensors are powered by battery and therefore any additional overhead may lead to shorter battery life, which can translate to additional costs in battery replacement.
In WiFi networks, the downlink traffic from an AP, e.g., a WiFi modem or router, to WiFi communications device or station (STA) is announced via a Traffic Indicator Map (TIM). Another characteristic of IEEE 802.11 of TGah (or 802.11ah) is the traffic patterns of various devices. Two main classes of devices are considered in TGah use case scenarios: the sensors and the offloading devices. The sensor networks usually have low duty cycle uplink (UL) traffic and occasionally downlink (DL) traffic, such as software uploads or some data request. The offloading devices have mainly DL traffic mixed with less UL traffic and tend to have non-uniform UL/DL short duration activity.
Information bits that are carried in WiFi communication packets or frames PHY preambles and decoded by receivers (sensor and offloading devices) are expensive (due to the limited number of bits carried in the PHY layer preamble), such as bits carried in a SIG field of a Physical Layer (PHY) preamble portion of the packet. Such information is also reliable due to its relatively low transmission rate, and therefore can be used to carry more important or crucial information. Careful design of fields or packet portions carrying such information, such as the SIG field, improves communications efficiency, such as in terms of lower power consumption.